Fine-grained agent for desulfurizing molten iron

Abstract

A fine-grained agent for desulfurizing molten iron comprising industrial calcium carbide, dried coal which contains at least 15% by weight of volatile constituents and which, immediately after being passed into the molten iron, releases at least 80 standard liters of gas per kg of coal, and optionally contains fine-grained magnesium. The coals used are lignites, flame coal, gas-flame coal, gas coal or coking coal. The agent is prepared by addition of the dried coal to the calcium carbide, if appropriate, pre-crushed, and common comminuted to a grain size of 90% <200 mu m. The fine-grained magnesium is present in the agent either in uniform distribution, or it is stored and fluidized separately from the carbide/coal mixture and added to the carbide/coal mixture in the transport line or in the lance, if appropriate, with variation during injection.

What is claimed is: 
     
       1. A fine-grain agent for the desulfurization of molten iron, which is based on calcium carbide and which is injected in fluidized form into an iron melt by means of a gas, the agent consisting essentially of industrial calcium carbide and a dried coal which contains at least 15% by weight of volatile components and which evolves a gas volume of at least 80 standard liters of gas/kg of coal at the temperature of the iron melt. 
     
     
       2. An agent as claimed in claim 1, which contains 50 to 98% by weight of calcium carbide and 50 to 2% by weight of coal. 
     
     
       3. An agent as claimed in claim 2, which contains 80 to 96% by weight of calcium carbide and 20 to 4% by weight of coal. 
     
     
       4. An agent as claimed in claim 1, wherein the coal is dried coal and the moisture content of the dried coal is less than 0.5% by weight. 
     
     
       5. An agent as claimed in claim 1, wherein about 90% by weight of the volatile components are evolved within less than 60 seconds, at a heating rate of the coal of 10 3  to 10 6  ° C./second, at the temperature of the iron melt. 
     
     
       6. An agent as claimed in claim 1, wherein about 90% by weight of the volatile components are evolved within less than 40 seconds, at a heating rate of the coal of 10 3  to 10 6  ° C./second, at the temperature of the iron melt. 
     
     
       7. An agent as claimed in claim 1, wherein the volatile components of the coal are evolved within less than 10 seconds at the temperature of the iron melt. 
     
     
       8. An agent as claimed in claim 1, which further consisting essentially of magnesium. 
     
     
       9. An agent as claimed in claim 8, which contains 47.5 to 95.5% by weight of calcium carbide, 50 to 2% by weight of coal and 2.5 to 40% by weight of magnesium. 
     
     
       10. An agent as claimed in claim 9, wherein the industrial calcium carbide content is 66 to 86% by weight, the coal content, on a dry basis, is 20 to 4% by weight and the magnesium content is 10 to 30% by weight. 
     
     
       11. The agent as claimed in claim 1, wherein the coal, on a dry basis, contains at least 25% by weight of volatile components. 
     
     
       12. An agent as claimed in claim 1, wherein the coal evolves a gas volume of at least 150 standard liters/kg of coal. 
     
     
       13. An agent as claimed in claim 1, wherein the coal is a lignite. 
     
     
       14. An agent as claimed in claim 1, wherein the coal is selected from the group consisting of flame coal, gas-flame coal and gas coal. 
     
     
       15. An agent as claimed in claim 1, wherein at least 90% by weight of the agent has a grain size of <200 μm. 
     
     
       16. An agent as claimed in claim 1, wherein at least 90% by weight of the agent has a grain size of <100 μm and 40 to 60% by weight of the agent has a grain size of <50 μm. 
     
     
       17. An agent as claimed in claim 1, which further comprises 1 to 10% by weight of fluorspar. 
     
     
       18. An agent as claimed in claim 17, which comprises 2 to 6% by weight of fluorspar. 
     
     
       19. A process for the preparation of the agent as claimed in claim 1, comprising drying coal, adding pre-crushed calcium carbide and grinding the mixture to the desired degree of fineness in a mill. 
     
     
       20. A process for desulfurizing molten iron comprising injecting in fluidized form the agent as claimed in claim 1 with a carrier gas rate of 3 to 30 standard liters/kg of agent into an iron melt. 
     
     
       21. A process as claimed in claim 20, wherein the agent is injected into the iron melt with a feed rate of 10 to 100 kg/minute. 
     
     
       22. A process as claimed in claim 21, wherein at least one non-oxidizing gas selected from the group consisting of nitrogen and argon is used as the carrier gas.